Path analysis was performed on eight morphometric attributes to determine for body mass of Macrobrachium nipponense, which were closed cultured for five years in ponds. The direct and indirect effects of eight attributes included total length, body length, carapace length, carapace width, carapace height, abdomen length, second uromere width and height. Results showed that body mass still had the greatest selection potential. And body mass was significantly correlated with the traits of total length, body length, abdomen length, carapace height and carapace width in female, and with traits of the total length and carapace height in male. Furthermore, body length and total length had substantial direct effects on body mass in female and male respectively. The regression equations were established between the selected traits to body mass for the male and female and the regression coefficient of equations reached the extreme significant level. The multiple correlation coefficients of the five attributes in female prawn and two attributes in male prawn to body mass reached 0.933 and 0.930 respectively, which indicated that the selected traits were the main variable index of body mass. Results suggest that body length in female and total length in male are primary selection criteria for improving body mass in M.nipponense.